We went to Marmaris last year but would definitely not return, for it is far too commercialised and loud, okay if you are just looking for a boozy, Blackpool-in-the-sun, type of holiday, but not for the holidaymaker looking for a more laid-back, relaxing, or typically Turkish resort.
However, we spent every day in nearby Icmeler, which we definitely would return to, for it was quieter, had better beaches, and a beautiful 'national park' consisting of pine forests surrounding it.
I suppose it all depends what you prefer.
For us there is no competition, Icmeler wins hands down every time!!!